Atlas Sound 70.7V, 100V Subwoofers and the Inverse Square Law, Amplifier Low Frequency Capability

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Subwoofers and the Inverse Square Law				Amplifier Low Frequency Capability
Even though frequencies below 200Hz are relatively omni-directional,				Many 70.7V / 100V power amplifiers on the market today are from the
listeners can still "localize" the subwoofer from the volume produced. To				era when business music systems extending down to only 100Hz were
avoid "hot spots" it may be necessary to use two or more subwoofers				widely accepted. These less expensive amplifiers are not capable of
tapped at a lower setting spread throughout the room instead of a single				driving today's high fidelity systems that require sound below 100Hz.
subwoofer tapped at maximum wattage.				When specifying the Atlas Sound FAPSUB, which operates well below
Ratio of Subwoofers to Full Range Speakers				100Hz, it is VERY IMPORTANT to use a power amplifier capable of full
				output down to and below the lowest frequency going INTO the amp,
Due to the many potential variables, it is difficult to give accurate sugges-				which is often around 50Hz. An amplifier with low-frequency capability is
				absolutely crucial whenever the system includes a subwoofer and is very
tions on system design. It is important for the system designer to look at
				important for today's high fidelity business music systems.
the required SPL at ear level, ambient noise in the room, speaker / trans-
former efficiency, and transformer insertion loss to determine the num-				Architect & Engineer Specficiations
ber of speakers and amplifier power required. In 70.7V / 100V systems,
care should be taken so the total speaker power taps do not exceed the				The loudspeaker system shall be Atlas Sound FAPSUB or approved equal.
amplifier's 70.7V output capability.				System shall include a high performance 8" subwoofer loudspeaker,
		(preliminary)
The following “rule of thumb” information and examples are offered to				ported bass reflex enclosure, and stud mount grille for conventional ceil-
provide a starting point for system design.				ing installation.
For “good” low frequency augmentation in a full range system (all full				Frequency response for the system shall be 45Hz – 120Hz (±10dB) and
range speakers and FAPSUBs on the same amplifier), a single FAPSUB				the sensitivity shall be 89dB (SPL at 1W / 1M).
should be used for every four full range speakers.				Loudspeaker shall be comprised of an 8" low frequency cone type driver.
For “excellent” low frequency augmentation in a full range system				Magnet shall be a minimum of 20oz (580g) and the voice coil diameter
(all full range speakers and FAPSUBs on the same amplifier), a single				shall be 1". Transformer shall be 70.7V with p ima taps at 1.9, 3.8, 7.5,
FAPSUB should be used for every two full range speakers.				15, 30, and 60 watts. A front mount tap selector switch shall be included.
				This switch shall have tr nsfo mer byp ss setting for 8Ω / direct cou-
Amplifier Limitations				pled operation
Even with the extreme efficiency of the FAPSUB it will not overcome the				Enclosure shall be a deep dr wn, 937 in3, steel enclosure design. To
limitations of an underpowered system. Be sure to allow sufficient head-				facilitate connection in co duit systems, enclosure shall be equipped
room by using basic system design parameters in choosing an amplifier.				with an access pa el coveri g a recessed terminal cup. This cover shall
				provide a comb at on 3⁄4" (19mm i side diameter) / 1" (25mm inside diam-
Example	Small Sports Bar			eter) knock-out on the s de access a d a top access compression fitting
Square Feet	1,500			/ strain relief to fac l tate flex ble conduit up to 22mm outside diameter
Ceiling Height	9'			or 1" (25mm ns de d ameter) conduit when the compression fitting is
Peak Ambient Noise Level	75 dB			re	oved.
Program	Digital Music			External wiring shall be accomplished via a removable, lockable wiring
Full Range Speakers				connector w th screw-down terminals to provide both secure wire
				ter	nat on and prewiring capability before loudspeaker installation.
Eight Atlas Sound FAP42T speakers tapped at 4 watts each (32 watts				The 4 po e ock ng Phoenix Style / Euro connector shall facilitate in/out
total) will provide 90dB on axis at 3.5' ear height (15dB above ambient).
				connect ons and shall be located in the recessed area behind the conduit
13.5' spacing between speakers provides minimum overlap coverage at
				acc	ss panel.
4kHz.
Subwoofers				S ismic support eye shall be provided on top of enclosure for additional
				susp nsion point when used in drop tile ceilings. Construction of enclo-
Two Atlas Sound FAPSUB subwoofers tapped at 30 watts each (60 watts				sure shall be a minimum of 18-gauge deep drawn galvanized metal.
total) will fill out the low frequencies at 8dB above the level of the full				The system shall include a support backing plate to reinforce the ceil-
range speakers. If boundary loaded into one corner of the			oom the level	ing material and tile support rails for use on either 2' x 4' (609mm x
will be increased another 6dB (14dB above the full range s			eakers).	1219mm) or 2' x 2' (609mm x 609mm) suspended ceiling tiles. This
Total Wattage: 92 watts x 1.3 Multiplier for headroom) = 119.6 watts				assembly can all be installed from beneath the ceiling tile.
Amplifier Power Suggested: 120 Watts Atlas Sound AA120				Overall front face diameter shall not exceed 153⁄4" (400mm); overall depth
				from the bottom of the ceiling shall not exceed 123⁄4" (323mm). Grilles

shall be press fit installation, manufactured 24-gauge (perforated mesh) and finished in white epoxy.

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